Adelaide Chronic Fatigue Syndrome Research Group
Exercise Physiology Research Unit,
Department of Physiology,
University of Adelaide,
South Australia

Excess lactic acid is not a cause of fatigue in Chronic Fatigue Syndrome

It is commonly assumed that the restricted life-style of CFS patients leads to a progressive reduction in physical fitness, perpetuating the exercise-induced fatigue and prolonging the illness. It is on this basis that both the Australian and British Colleges of Physicians recommend exercise training programs as a cornerstone of patient management. Physical fitness is best assessed from such parameters as maximal oxygen uptake and maximal heart rate, measured during controlled exercise tests. After a recent series of exercise tests in ~50 CFS patients we reported values which were not different from those expected in healthy, sedentary members of the general community (Sargent et al., 1999, 2001). This study was conducted in male and female CFS patients with mean KPS scores of 73.6 and 63.3, respectively, implying a moderately severe illness with the patients being able to "....care for themselves but unable to carry on normal activity or to do active work". Our conclusion from this study was that patients with CFS have normal physical fitness and that there is no physiological basis for recommending graded exercise training programs in the treatment of this condition. Therefore, some other explanation must be sought to explain the excessive fatigue, both during and after exercise, which is such a classical feature of CFS. Early work from our laboratory and others (Wong et al., 1992; Lane et al., 1994) suggested that excessive lactic acid accumulation might be a factor in the muscle pain and fatigue experienced by CFS patients during exercise. We have now completed an investigation of plasma lactate responses during incremental exercise to volitional exhaustion in 16 male and 17 female CFS patients and their gender-, age- and mass-matched sedentary controls. In both male and female CFS patients, the exercise time to exhaustion and the peak power output at exhaustion were lower in the CFS patients. However, the increases in plasma lactate concentration with exercise intensity in both genders were not different from control subjects nor were peak lactate or the calculated lactate threshold and associated metabolic parameters. These results indicate that the production and clearance of lactic acid in CFS patients is normal and does not contribute to their earlier fatigue and reduced power output during exercise.